chve
member
Reged: 11/12/06
Posts: 49
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Can someone plz outline the differences between these two types of focusers?
I am looking for a first scope - this is the main difference between the two scopes I am looking at - Orion XT10, and a Zhumell 10" Dob.
Thanks in advance for your help!!
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dgs©
Postmaster
Reged: 03/29/04
Posts: 13899
Loc: West Monroe, Louisiana
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The crayford is a friction drive (no gear teeth... smooth spindle turns against smooth flat in side of drawtube). There are two sets of needle bearings on the far side of the focuser drawtube from the focus spindle. The focus spindle is pressed against the side of the drawtube and keeps it, in turn, pressed against the bearings on the far side. This keeps the tube from shifting alignment while focusing (no image shift). The pressure against the focusing spindle is enough to keep the friction forces high enough to keep the tube from slipping.
That's it in a nutshell. The crayford is really smooth and free of image shift that so many R&P focusers are plagued with. If you don't get the Crayford, you will eventually upgrade your focuser. 
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- david
8"Ø Newtonian on SVP, Moonlite CR2, Telrad
PST Oberwerk Ultra 15x70 Orion Ultraview 10×50
Hand-me-down Sears Refractor (Discoverer) 60mm×900mm
"What we have done for ourselves alone dies with us; what we have done for others and the world, remains and is immortal." --Albert Pike
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sixela
Postmaster
Reged: 12/23/04
Posts: 9499
Loc: Boechout, Belgium
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Quote:
Can someone plz outline the differences between these two types of focusers?
I am looking for a first scope - this is the main difference between the two scopes I am looking at - Orion XT10, and a Zhumell 10" Dob.
Thanks in advance for your help!!
Note that in the US, the XT10i (Intelliscope) comes with a Crayford, too, these days.
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400mm f/4.46 David Lukehurst truss Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
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chve
member
Reged: 11/12/06
Posts: 49
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What does this upgrade typically run?
I've been searching the sites I'm looking for scopes, and there nothing.
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 12068
Loc: Rockford Illinois
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All of the Orion Dobs 8" and larger come with the Crayford now.
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Neo... (Jeff)
-=-=-=-=-=-=-
10" LX200-GPS/SMT UHTC "Draco"
 Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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chve
member
Reged: 11/12/06
Posts: 49
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The Skyquest XT classic (black tube) still lists the focuser as a rack and pinion.
I'm not comparing the Intelliscope, it's the Classic.
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Talstarone
Vendor (Inner Planetary Products)
Reged: 09/12/06
Posts: 7592
Loc: Benson, North Carolina
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The latest Orion Ad on the inside back cover of January's Sky and Telescope says
very clearly: That the Crayford focuser upgrade applies to the IntelliScope Line of Dobs only. It does not apply to the XT Classic series of Dobs.
I know that in catalogs they listed the upgrades for the Classics as well, but it seems to have not taken place.
I put a call in to Orion yesterday, and was told the catalog stating the Crayfords would be included on the XT Classic Scopes was an error.
They may have thought about adding them earlier on, but as of for now, they will only be standard on the XTi series od Dob scopes.
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Todd C.
Celestron NexStar 4SE(102mm F/13)Maksutov-Cass
Meade ETX-80AT(80mm F/5)Achro Refractor
Meade ETX-60BB(60mm F/5.8)Achro Refractor
www.innerplanetaryproducts.com
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"Outer Space at Down to Earth Prices"
Edited by Talstarone (12/07/06 06:18 PM)
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Talstarone
Vendor (Inner Planetary Products)
Reged: 09/12/06
Posts: 7592
Loc: Benson, North Carolina
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Chve, if the Zhumell offers the Crayford focuser, along with its $499.00 price at www.telescopes.com, then I would choose the Zhumell with little hesitation.
It is a great performing Dob and the addition of a Crayford focuser alone would be enough to make the desicion for me.
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Todd C.
Celestron NexStar 4SE(102mm F/13)Maksutov-Cass
Meade ETX-80AT(80mm F/5)Achro Refractor
Meade ETX-60BB(60mm F/5.8)Achro Refractor
www.innerplanetaryproducts.com
Meteorites and More....
"Outer Space at Down to Earth Prices"
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sixela
Postmaster
Reged: 12/23/04
Posts: 9499
Loc: Boechout, Belgium
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Yup. It's pretty much a no-brainer. If you want Intelliscope, get an XT10i, and if you don't, get a Zhumell. In both cases you'll have a Crayford focuser.
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400mm f/4.46 David Lukehurst truss Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
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firestar
Born to be Mild
Reged: 10/18/06
Posts: 3942
Loc: Cleveland Ohio USA
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http://www.clearvueoptics.com/focusers.htm
The upgrades start at about $150,its great when the scope comes with them.
The zhumell with crayford and free shipping is a fantastic deal.
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Eastlake Ohio
Lots of cheap Asian glass  
Antares 12" Dob,Antares 8" Dob
Meade 8" SCT, Celestron C8 SCT
Zhumell 152 mm F8,Antares 127 mm f9.4
Orion short tube 90 F5.6,Celestron 80 ED F7.5
Imaging Source DMK 21AU04 ccd camera
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chve
member
Reged: 11/12/06
Posts: 49
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Thanks firestar - that helps!!
I was having a hard time locating just the upgrade, probably going to end w/ the Zhumell. There is a used XT I've got my eye on as well, it has a r & p focuser so this info will help in my decision making process.
Thanks Everyone for your help!!
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Art Bianconi
Post Laureate
Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
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From a performance perspective, even the worst Crayford will outperform a rack and pinion focuser. It's not even a contest. Smoothness of operation, precision in focusing, maintaining coaxial alignment and consistency of behavior.
Greased racks for example attract dust or grit and the moment that piece gets ground into the gear, things change. Adjusting the focuser is always a compromise between eliminating sloppy optical tolerances vs. freedom of movement.
R&P focusers can offer longer travel which may be of some value in refractors. R&P focusers are most often lighter too when compared to the bulk of a CNC machined Crayford type. The better Crayford's offer dual speed focus and 1.25 to 2" adaptors. I've yet to see dual speed on garden variety R&P focusers.
Lastly, price! It takes a fair amount of materials and manufacturing to produce a finished Crayford, far more than a rack & pinion unit and that will manifest itself as a higher entry fee. However, when you factor in the likelihood of throwing away the R&P focuser, getting the Crayford at the onset is actually saving you money. I am seeing a sudden influx of Crayford's made off shore. The Asians have discovered the Crayford so prices for some will be sure to challenge what is charged for R&P focusers. Just be careful of what you are getting.
Hope this helps some.
Art
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“Everything is on its way to somewhere. . . . . everything!"
____________________ George Malley (John Travolta)
________________________ "Phenomenon"
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sixela
Postmaster
Reged: 12/23/04
Posts: 9499
Loc: Boechout, Belgium
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Quote:
From a performance perspective, even the worst Crayford will outperform a rack and pinion focuser.
Not necessarily (I've seen rack and pinion focusers that were better than my Crayford focuser as it came out of the box), but a bad Crayford is something you can shim to perfection yourself; it's a lot easier to shim the roller bearing assembly so its plane is parallel to the focuser axis and so that the draw tube presses on the actuator axis than to machine a new rack or pinion to precise mechanical tolerances  .
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400mm f/4.46 David Lukehurst truss Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
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Jon Isaacs
Postmaster
Reged: 06/16/04
Posts: 12070
Loc: San Diego, California
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I was having a hard time locating just the upgrade, probably going to end w/ the Zhumell. There is a used XT I've got my eye on as well, it has a r & p focuser so this info will help in my decision making process.
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Orion has a replace Crayford for $70.
Jon
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Jon Isaacs
Postmaster
Reged: 06/16/04
Posts: 12070
Loc: San Diego, California
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>>>From a performance perspective, even the worst Crayford will outperform a rack and pinion focuser. It's not even a contest. Smoothness of operation, precision in focusing, maintaining coaxial alignment and consistency of behavior.
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I think that is a bit extreme... There are good rack and pinion focusers available, it is just more difficult to make a good rack and pinion focuser than it is a good crayford.
A good rack and pinion focuser can be all that is needed to get a good sharp image, free from rock and play and yet have a nice smooth action. The standard Asian Rack and pinion focusers can be reworked so they are decent...
When I think of some of the poor focusers I have used, I have to say I am pretty happy with the garden Variety Asian Rack and Pinions once they are setup properly.
Jon Isaacs
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Talstarone
Vendor (Inner Planetary Products)
Reged: 09/12/06
Posts: 7592
Loc: Benson, North Carolina
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I personally prefer the Crayford Style Focusers myself. But I also haven't had the pleasure of trying a true high end rack and pinion focuser.
It seems the rack and pinion focusers found on Takahashi Telescopes are extremely good quality, or I dont think Tak would include them on their refractors. So, there are great rack and pinion focusers out there.
But in our price range a typical Crayford Focuser will out perform any of the Rack and Pinion Focusers available.
So, if you are looking at both scopes, and you know you will have to replace the standard rack and pinion focuser in the Orion, you may as well add $70.00 to the price of the Orion. As well as adding the time it takes you to make the install.
I agree with the majority in this case. If the Zhumell comes with a Crayford Focuser and is Brand New, it would easily be my first choice.
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Todd C.
Celestron NexStar 4SE(102mm F/13)Maksutov-Cass
Meade ETX-80AT(80mm F/5)Achro Refractor
Meade ETX-60BB(60mm F/5.8)Achro Refractor
www.innerplanetaryproducts.com
Meteorites and More....
"Outer Space at Down to Earth Prices"
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Mike Moffatt
scholastic sledgehammer
Reged: 07/13/05
Posts: 856
Loc: Broken Arrow, Oklahoma
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Quote:
I've yet to see dual speed on garden variety R&P focusers.
This knob which is now on my home made crayford was first made for my cheap garden variety Orion R&P focuser, giving me dual speed. Factory small knob on one side and larger fine focus knob on the other.
It now is the only knob on my crayford.
Granted Art, you were refering to factory two speed R&P focusers but it never hurts to inspire a little DIY in the beginners forum.
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Mortal as I am, I know that I am born for a day. But when I follow at my pleasure the serried multitude of the stars in their circular course, my feet no longer touch the earth.
- Ptolemy,c.150 AD
Mike Moffatt
6" f8 Coopered Newt/Dob
15x70 Celstron Skymasters
www.tulsawalk.com/telescope
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Rusty
Postmaster
Reged: 08/06/03
Posts: 16399
Loc: Brooker, FL
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There are two basic designs to the rack-and-pinion focuser. The cheaper - and lesser performing - ones use straight cut teeth. The upscale ones are as good as good Crayfords, because they use helical-cut teeth. Both my gone SV-105 and present TOA-130 use the latter, and they're both superb.
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N11GPS Fastar
TOA-130S
MK66 Std
Vintage C5
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WNB
member
Reged: 03/10/07
Posts: 36
Loc: NW England
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OOPS
sorry for any offence.
goodbye
Edited by WNB (03/15/07 12:17 PM)
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sixela
Postmaster
Reged: 12/23/04
Posts: 9499
Loc: Boechout, Belgium
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http://www.tomhole.com/Focuser.htm
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400mm f/4.46 David Lukehurst truss Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
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